Can't find Mega Stones in Pokemon X & Y? Follow these directions for Mega Stone success!

Before you can collect a Mega Stone, you have to get the Mega Ring first. After this, some Mega Stones will be granted to you, or you need to collect them separately.

Stones found after defeating the Elite Four can only be collected between 8:00pm-9:00pm and you'll pick where they are straight away as there is a sparkly spot where the Mega Stone is hiding.

Charizard, Blastoise and Venusaur Mega Stones: Professor Sycamore grants these stones when you pick your second starter character. Can't wait? Buy them from the Vernal Anue Stone Emporium in Lumiose City.
Abomasnow Mega Stone: Talk to Abomasnow (at the end of the Frozen Cavern) and he will give you the stone.
Absol Mega Stone: You get this stone in Kiloude City after defeating the Elite Four.
Aerodactyl Mega Stone: Get this in Ambrette Town.
Aggron Mega Stone: This is in Pokemon Y only, and you get it in Cyllage Gym after defeating the Elite Four.
Alakazam Mega Stone: Find this in the B3F level of the Reflecting Cave after beating the Elite Four.
Ampharos Mega Stone: You'll get this in Azure Bay.
Banette Mega Stone: Find this in the Cave of Emptiness after defeating the Elite Four.
Garchomp Mega Stone: Find this in Victory Road after defeating the Elite Four.
Gardevoir Mega Stone: In the Southern Boulevard of Lumoise City, there’s a café. Trade for a Ralts (which will be holding a mega stone).
Gengar Mega Stone: You'll get given this in Laverre City.
Gyrados Mega Stone: Find this in Couriway Town after beating the Elite Four.
Heracross Mega Stone: Pokemon Y only - it can be found in Santalune Forest and can only be found after beating the Elite Four.
Houndoom Mega Stone: This is only available in Pokemon Y and can be found on Route 16.
Khangaskhan Mega Stone: Find this in the Glittering Cave after defeating the Elite Four.
Lucario Mega Stone: This will be given to you when you are given the Lucario.
Manectric Mega Stone: Pokemon X only - Find this on Route 16 after beating the Elite Four.
Mawile Mega Stone: Find this in Shabboneau Castle after beating the Elite Four.
Medicham Mega Stone: Find this in Laverre City after beating the Elite Four.
Mewtwo Mega Stone: Find this in the Unknown Cave near the Pokemon Village after beating the Elite Four.
Pinsir Mega Stone: Pokemon X only - find this in Santalune Forest after beating the Elite Four.
Scizor Mega Stone: Find this in the Frozen Cavern behind Abomasnow.
Tyranitar Mega Stone: Pokemon X only - find this in Cyllage Gym after beating the Elite Four.